1. Field of the Invention
The present invention relates to a throttle valve opening controller for applying retarding forces against the closing force of the throttle valve at the time of quick closing thereof. More particularly, this invention relates to an improved throttle valve opening controller, which is suitable for use in internal combustion engines of automobiles equipped with exhaust gas purifying devices, and is provided with a diaphragm device consisting of a diaphragm which is movable in association with the throttle valve when the opening of said throttle valve is smaller than the specified value, a spring for urging said diaphragm with a force smaller than the closing force of the throttle valve, and a diaphragm chamber which is formed in the rear of said diaphragm and to which atmospheric pressure or intake vacuum immediately downstream of the throttle valve is admitted.
2. Description of the Prior Art
Generally, injurious exhaust gases from internal combustion engines, such as automobile engines, include hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx). Of these exhaust components, hydrocarbons are formed as a result of incomplete combustion, flame suppression at inner wall surfaces of the combustion chambers or misfire. In particular, when the throttle valve is closed fully and quickly at the time of engine brake application or for any other reasons, the negative pressure in the intake pipe increases abruptly, and therefore the fuel adhering to the intake manifold evaporates quickly and the evaporated fuel is sucked into the combustion chamber of the engine in large quantities. In addition, as the absolute amount of air being sucked becomes insufficient, ignition becomes inferior, resulting in a misfire or near-misfire. Under this condition, unburned fuel is discharged as hydrocarbons in large quantities. To prevent the emission of hydrocarbons when the engine brake is applied, deceleration control devices, such as throttle positioner and dash pot, have been proposed. These devices are designed to reduce the formation of hydrocarbons through the improvement of combustion and the prevention of misfire by preventing the air-fuel mixture from becoming too rich and maintaining a certain amount of air-fuel mixture at the time of deceleration.
As shown in FIG. 1, such a device comprises, for example, a diaphragm device 18 which is designed to apply retarding forces against the closing force of a throttle valve 16 disposed downstream of a venturi 14 in an intake passage 12 of a main body of carburetor 10 at the time of quick closing thereof. This diaphragm device consists of a diaphragm 18a which is in abutting contact with a throttle valve lever 17 rotatable together with the throttle valve 16 through a rod 24 at the tip thereof and is movable in association with the throttle valve 16 when the opening of the throttle valve 16 is smaller than the specified value, a compression spring 18c for urging said diaphragm 18a with a force smaller than the closing force of the throttle valve, and a diaphragm chamber 18b which is formed in the rear of said diaphragm 18a and to which atmospheric pressure is admitted from an air port 22 disposed upstream of the venturi 14 through a pressure transmitting valve (hereinafter referred to briefly as PTV) 20. The PTV 20 has a check valve 20a and an orifice 20b which are connected to each other in parallel. The check valve 20a is arranged in such a direction that the atmospheric pressure admitted from the air port 22 can be rapidly transmitted to the diaphragm chamber 18b of the diaphragm device 18. In FIG. 1, numeral 26 designates an air cleaner for admitting clean air to the intake passage 12, while numeral 28 indicates an intake manifold for distributing and supplying the air-fuel mixture produced in the main body of carburetor 10 to the combustion chambers of the engine.
In conventional deceleration control devices as described above, when the engine is stopped, the force of the return spring of the throttle valve 16 for applying the closing force to said throttle valve 16 is larger than the force of the compression spring 18c of the diaphragm device 18. Accordingly, the rod 24 is pushed back to the right in FIG. 1 by the throttle valve lever 17, overcoming the force of the compression spring 18c, thus keeping the throttle valve 16 in the fully closed condition or in the specified idling opening. When the engine is operated, the throttle valve 16 is opened in association with the accelerator not shown. Under this condition, the throttle valve lever 17 is disengaged from the rod 24 and the rod 24 is pushed forward to the specified position by the actions of the compression spring 18c and the air admitted quickly to the diaphragm chamber 18b through the air port 22 and the PTV 20. If the accelerator is suddenly closed at the time of deceleration or for any other reasons and a closing force is applied to the throttle valve 16, the throttle 16 is turned in the closing direction by the force of the return spring thereof. When the opening of the throttle valve 16 has been decreased to such an extent that the throttle valve lever 17 reaches the position where it comes into abutting contact with the rod 24, a retarding force is applied to the throttle valve lever 17 of the throttle valve 16 through the rod 24 by the actions of the compression spring 18c and the air pressure accumulated in the diaphragm chamber 18b. Accordingly, the quick closing of the throttle valve 16 is prevented, and the throttle valve 16 is closed progressively by the force of the return spring of the throttle valve 16 which overcomes the force of the compression spring 18c and the air pressure in the diaphragm chamber 18b. At this time, the operating characteristics of the diaphragm 18a of the diaphragm device 18, i.e., the opening control of the throttle valve 16 is dependent upon the conditions of the air which flows backward toward the air port 22 from the diaphragm chamber 18b of the diaphragm device 18 through the orifice 20b of the PTV 20. As the quick closing of the throttle valve 16 is prevented by the diaphragm device 18 as described above, the sudden increase in negative pressure in the intake manifold 28 is prevented and a certain ratio of air-fuel mixture is secured. As a result, combustion is improved and misfire is prevented, thus reducing the formation of hydrocarbons.
In internal combustion engines, on the other hand, the opening of the throttle valve to be maintained at the time of deceleration varies with the running conditions in general. For example, the frictional forces to be developed in the internal combustion engine in the cold state differs from that in the warmed-up engine even if the throttle valve opening is the same. Accordingly, the performance of engine brake is varied. And in the internal combustion engines provided with a catalytic converter as an exhaust purifying device in the exhaust system, the formation of hydrocarbons should be reduced by increasing the opening of the throttle valve maintained at the time of deceleration when the engine is in the cold state and a temperature of the catalytic converter has not reached a level at which its purifying performance is fully exhibited. After the engine has been sufficiently warmed up to a temperature level at which the catalytic converter fully exhibits the purifying performance, it is desirable to leave the reduction of exhaust of hydrocarbons to the catalytic converter and to decrease the throttle valve opening in order to prevent increased fuel cost and improve the enging brake performance, thereby improving the running performance of the vehicle.
With conventional deceleration control devices, however, the operating characteristics of the diaphragm device are the same, regardless of the running conditions of the engine and these devices have a disadvantage that the problems of the running performance of the vehicle, exhaust gas purification and fuel cost are not sufficiently solved either in the cold state or in the warmed-up condition of the engine.